Pregnancy outcome after first-trimester exposure to fosfomycin for the treatment of urinary tract infection: an observational cohort study

Purpose The primary aim of our study was to assess pregnancy outcome after first-trimester exposure to fosfomycin. Methods We performed an observational cohort study analysing prospectively ascertained pregnancies including 152 women exposed to fosfomycin in the first trimester of pregnancy in comparison with a randomly selected cohort comprising 456 pregnancies not exposed to fosfomycin. All pregnancies were identified through risk consultations using structured questionnaires between January 2000 and December 2016 by the German Embryotox pharmacovigilance institute in Berlin. Primary objectives were the risks of major birth defects and spontaneous abortion. Results Only 1 out of 146 exposed infants was affected by a major birth defect (0.7%, 95% CI 0.04-4.33%) in comparison to 15/399 in the non-exposed cohort (3.8%, 95% CI 2.2-6.26%). Spontaneous abortions were observed in 5/152 cases in the fosfomycin cohort vs. 53/456 cases in the comparison cohort (cumulative incidence 6.2% vs. 23.1%; HR adjusted 0.35, 95% CI 0.14-0.90). Conclusion This is the first study specifically examining the teratogenic risk of fosfomycin. The study results do not indicate an increased risk of adverse pregnancy outcome after fosfomycin exposure during early pregnancy. However, larger studies are needed to confirm the safety of fosfomycin during the first trimester.